Device for shifting a propeller into reverse, comprising an actuator acting on a crank pin

The field of the present invention is that of aeronautical turbomachines and, more particularly, that of turbine engines with unshrouded propellers referred to as “open rotor” or high-speed-propeller engines and that of the devices for controlling the orientation of the blades of such propellers.

Aeronautical engine technology is evolving rapidly and one of the avenues being explored in an attempt to improve the specific fuel consumption of civilian aircraft engines is currently that of developing open-rotor engines. Such engines, like the one described in patent application FR2941493 by the applicant company, comprise a conventional turbine engine gas generator, one or more turbine stages of which driving an unshrouded fan extending on the outside of the engine. For reasons concerned with the level of thrust to be achieved and in order to reduce the noise generated by the blades, the engine generally has two contra-rotating unshrouded propellers, which means two propellers which rotate in opposite directions and which are situated downstream of the engine in order to keep them as far away as possible from the passenger cabin. The overall configuration of an open-rotor engine is given in <figref idref="DRAWINGS">FIG. 1</figref>.

As is the case in conventional turboprop engines, the blades of the propellers of the open rotors are variable-pitch blades, which means that the pitch of these propellers can be modified during flight in order to alter the thrust generated by the engine and optimize the efficiency of the propeller to suit the speed of the aircraft. Numerous devices have been designed for varying the pitch of the blades and these generally involve rotating the blade about its main axis using bevel gears situated under the blade root, and collaborating with bevel gears belonging to a control system. One example of these devices is given in UK document GB 2218747.

One of the constraints on the propeller blade pitch adjustment control systems is that these blades have to be able to be brought into what is known as the “feathered” position in the event of system failure. The feathered position involves rotating the propeller until its chord is more or less aligned with the direction of the wind, thus minimizing the drag that it generates and, therefore, minimizing the yaw instability induced on the aircraft. The feathered position needs to correspond to a position of equilibrium automatically adopted by the propeller when the pitch control system is no longer transmitting torque. To achieve that, counterbalancing bob weights are generally attached to the bevel gears of the control system and positioned to project in cantilevered manner beyond these. In normal operation, they are held in position by the control system. If this system fails, the action of centrifugal force caused by the rotation of the propeller drives them toward a rest position which corresponds to the position for feathering the blade.

In normal use, during flight phases, the pitch of a propeller changes between two end points corresponding to a low-pitch position at low forward speed, of the order of 30° with respect to the plane of rotation of the propellers, and a high-pitch position at high speed, which is of the order of 65° with respect to this same plane of rotation of the propellers. The feathered position corresponds to a pitch setting higher than that of the high pitch setting and equal to around 90°. Pitch settings under these normal conditions of use are, by convention, referred to as positive pitch settings.

Following landing, the aircraft needs to be slowed down in order to reduce the distance that it rolls and thus allow it to use shorter runways. To achieve that, the engines are put into a position known as the reverse position, which tends to direct their thrust toward the upstream end of the engine. In an open rotor engine, as is already the case with turboprop engines, reverse is obtained by applying a negative pitch angle to the propellers, i.e. by positioning the leading edge of the propeller blades in the rear sector with respect to the plane of rotation of the propeller. This position is obtained by continuing to rotate the propeller, about its longitudinal axis, beyond the low-pitch position until the zero-pitch position, i.e. the position in which the blades lie in the plane of rotation of the propeller, has been crossed and increasing the pitch to a set negative pitch value.

Commonly, the blade root bevel gear creates a reduction ratio of 2 between the pitch angle of the counterweight and the pitch angle of the blade. As a result, rotating the propeller through 90° between the feathered and the zero-pitch position corresponds to the bob weights rotating through 180°, causing them to move from the upper, and therefore stable, vertical position of feathering into an unstable lower vertical position situated opposite the former position.

One of the problems that needs to be overcome in such engines, whether they be open rotor or turboprop engines, is that of ensuring that the bob weights do not remain in this unstable position when the pilot commands the shift into reverse, and that of being certain that the propeller blades are indeed in a negative-pitch position when the pilot reapplies power after landing. If such is not the case, the opening of the throttle will cause the engine to run away if the propellers are still at a zero pitch setting, with the risks of over speed and therefore blade breakage or even will result in the propellers applying traction if the pitch setting has remained in the positive pitch settings domain, even though the pilot was expecting these propellers to afford a braking action.

It is therefore important to make sure that the propellers do indeed shift beyond the zero-pitch position during a shift into reverse, i.e. that the bob weights do not remain in the unstable position located between the positive pitch settings and the negative pitch settings.

It is an object of the present invention to address these disadvantages by providing a device for controlling the pitch of a propeller which guarantees that the bob weights will shift beyond the zero-pitch position in the event of a demand to shift into reverse.

To this end, one subject of the invention is a device for controlling the shift into reverse of a propeller-type turbomachine, through action on a pitch control spindle that controls the pitch of said propellers, said device comprising at least one bob weight mounted with overhang on said control spindle and designed to drive said propellers toward their feathered position under the action of the centrifugal force generated by the rotation of the turbomachine, the device also comprising an actuator able to cause said control spindle to turn in order to shift the pitch of the blades from a traction mode to a reverse mode, passing via a zero-pitch position, characterized in that the bob weight is in a position of unstable equilibrium with respect to the action of the centrifugal force when said control spindle causes the pitch of the propellers to pass via the zero-pitch position.

Combining unstable equilibrium of the bob weight with the zero-pitch position of the propellers makes it possible to guarantee that the propellers will not remain in a zero-pitch position, as this could lead to engine failure if the pilot reopened the throttle in this position.

For preference, the device comprises an actuating means that applies a torque to said control spindle when the bob weight is in said position of unstable equilibrium, so as to prevent it from remaining in that position. The propellers will thus not return to traction mode as this configuration too would present a danger if the pilot opened the throttle believing the engine to be in reverse.

Advantageously, said actuating means applies a torque to said spindle both during the shift from traction mode to reverse mode and during the return from reverse mode to traction mode. This then guarantees that the propellers do actually shift to the desired configuration, whether this be reverse or traction.

For preference, the actuator applies no torque to said control spindle when the bob weights are in the position of unstable equilibrium. This configuration eliminates any possible interference between the torques applied to the control spindle by the device for shifting into reverse and by the actuator. It simplifies the development of the device for shifting into reverse.

In a preferred embodiment, said actuating means applies its torque to said control spindle via a crank pin mounted with freedom to rotate via one of its ends on said bob weight.

Advantageously, said actuating means is held at one of its ends by a pivot spindle offset parallel to the control spindle and is returned in rotation about this spindle, toward the crank pin, via means that creates a return torque.

For preference, the crank pin at its free end bears a transfer means able to collaborate with said actuating means so as to transfer the torque supplied by said actuating means to the control spindle.

In one particular embodiment, said actuating means is a tongue and the transfer means is a rod configured to slide along said tongue during the shift into reverse.

More preferably, said tongue at its free end comprises a retaining means able to limit the sliding of said rod along the tongue during the shift into reverse, so as to provide a purchase for said crank pin.

In a preferred embodiment, said rod is in abutment against said retaining means before said bob weight reaches its position of unstable equilibrium. Advantageously, as said bob weight enters its position of unstable equilibrium, the rod is in abutment against said retaining means and the crank pin is oriented in such a way as to push the bob weight beyond said unstable position.

In one particular embodiment, the control device comprises two actuating means such as described hereinabove, a first means applying a torque to the crank pin for the shift from the position of use to the reverse position and the second means applying a torque to said crank pin for the return to the position of use.

The invention also relates to a propeller for a turbomachine comprising a blade root equipped with a device for controlling the shift into reverse as described hereinabove, or even to a turbomachine comprising at least one such propeller.

The invention will be better understood and other objects, details, features and advantages thereof will become more clearly apparent during the course of the detailed explanatory description which will follow, of one purely illustrative and nonlimiting exemplary embodiment of the invention, given with reference to the attached schematic drawings.

In these drawings:

<figref idref="DRAWINGS">FIG. 1</figref> is a schematic view in cross section of a high-speed propeller turbine engine;

<figref idref="DRAWINGS">FIG. 2</figref> is a perspective view of a device for controlling the pitch of the blades of the turbine engine of <figref idref="DRAWINGS">FIG. 1</figref>, according to one embodiment of the invention;

<figref idref="DRAWINGS">FIG. 3</figref> is a detailed view showing the actuator of the control device of <figref idref="DRAWINGS">FIG. 2</figref>;

<figref idref="DRAWINGS">FIG. 4</figref> is a face-on view of the device of <figref idref="DRAWINGS">FIG. 2</figref>, the pitch of the propeller corresponding to the cruising position;

<figref idref="DRAWINGS">FIG. 5</figref> is a face-on view of the device of <figref idref="DRAWINGS">FIG. 2</figref>, the pitch of the propeller corresponding to the low-pitch position, the engine being at low idle on the ground;

<figref idref="DRAWINGS">FIGS. 6 to 8</figref> are successive face-on views of the device of <figref idref="DRAWINGS">FIG. 2</figref>, with the pitch of the propeller changing progressively from the low-pitch position of low idle on the ground to the position of low-pitch in reverse, and

<figref idref="DRAWINGS">FIG. 9</figref> is a face-on view of the device of <figref idref="DRAWINGS">FIG. 2</figref>, with the pitch of the propeller being in its final position, corresponding to a low pitch in reverse.

Reference is made to <figref idref="DRAWINGS">FIG. 1</figref> which shows a high-speed propeller turbine engine <b>1</b> comprising, on the one hand, a conventional gas generator consisting, among other things, of a compressor <b>2</b>, of a combustion chamber <b>3</b> and of a turbine <b>4</b> which drives the compressor <b>2</b> and, on the other hand, a free turbine <b>5</b> situated downstream of the coupled turbine <b>4</b>, which drives the two series of blades of the contra-rotating propellers <b>6</b>. The propellers are positioned on the outside of the casing <b>7</b> of the gas generator and their blades are held by a blade root <b>8</b> capable of rotating about an axis that is radial with respect to the turbomachine <b>1</b> and which passes through the center of the blade root and constitutes the main axis of the blade. The blade is rotated by an actuator, taking the form of a linkage <b>9</b>, which acts on a pair of bevel gears one of which is fixed to the blade, surrounding the blade root <b>8</b>. As indicated earlier, the size of these bevel gears gives rise to a reduction ratio of 2, such that the propeller describes the path between its feathered position and its zero-pitch position when the associated bob weights rotate through 180° C. A control system <b>10</b>, via the linkages <b>9</b>, controls the angular position of the blades of each of the propellers <b>6</b> and ensures that they rotate synchronously.

<figref idref="DRAWINGS">FIG. 2</figref> shows a protective enclosure <b>11</b> of the blade pitch control device according to the invention, which surrounds the blade root <b>8</b> and is fixed to the blade retaining ring <b>12</b>. This rotary ring secures the blades to the shaft of the engine and turns them to generate thrust. The enclosure <b>11</b> is essentially in the form of a cylinder surrounding the blade root <b>8</b> and comprising a lateral window from which a control spindle <b>13</b> emerges, this spindle bearing bevel gears which mesh with blade root bevel gears to control the pitch of the blade. Fixed to this spindle, to project in cantilevered manner beyond it, are bob weights <b>14</b> in the form of two angular sectors centered on the spindle, which are positioned side by side and fixed to a disk <b>15</b> push-fitted onto the support spindle <b>13</b>. These two sections are angularly positioned in such a way that, under the action of centrifugal force, they apply a torque that tends to cause the spindle <b>13</b> to rotate and thereby cause the blades of the propeller <b>6</b> to rotate toward their feathered position.

Reference is now made to <figref idref="DRAWINGS">FIG. 3</figref> which shows the device for controlling the pitch of the blades <b>6</b>. The linkage <b>9</b> is fixed, at its external end, to the bob weights <b>14</b> via a journal <b>16</b> which passes through the two bob weights, running parallel to the spindle <b>13</b> and offset laterally with respect to that spindle. The connection between the external end of the linkage <b>9</b> and the journal <b>16</b> is a connection with freedom to rotate about the journal, so that the linkage <b>9</b> can turn the bob weights <b>14</b> through its longitudinal movement, acting as a connecting link rod.

Each of the bob weights <b>14</b> also bears a spindle on which is mounted a crank pin <b>17</b> having the form of a metal strip able to rotate in a plane perpendicular to the control spindle <b>13</b>. The axis about which the crank pins rotate is positioned on the bisector of the angular sectors constituting the bob weights <b>14</b>, on the side external to the bob weights in order to give the crank pins <b>17</b> the longest possible level arm. The two crank pins <b>17</b> move about their common axis, remaining parallel to one another, their free ends being connected by a link rod <b>18</b> extending in the direction of the control spindle <b>13</b>.

At the same time, the retaining ring <b>12</b> bears, on each side of the root of the blade of the propeller <b>6</b>, two tongues <b>19</b>, i.e. two components in the shape of tabs which are fixed to the ring <b>12</b> by one of their ends, by means of a spindle <b>20</b> about which they can turn. It is possible to make out a first tongue <b>19</b><i>a </i>which acts during the shift into reverse and a second tongue <b>19</b><i>b </i>which itself acts during the return to normal operation. Torsion springs (not depicted), borne by these tongue spindles <b>20</b>, return the tongues toward the bob weights <b>14</b> and toward the median plane of the retaining ring <b>12</b>. The tongue spindles <b>20</b> are positioned on the retaining ring <b>12</b> on either side of the blade root, at points which are laterally separated with respect to the control spindle <b>13</b> so that the tongues face one another and, via their free end, butt against the bob weights <b>14</b> when there is no interference between them and the crank pins <b>17</b>. The tongues <b>19</b> each have a flat tab-like shape extending in a plane parallel to the control spindle <b>13</b>, from the spindles <b>20</b> as far as a free end <b>21</b> which is hooked. This hooked end is intended to act as an end stop to the link rod <b>18</b> when it slides along said tongue. The hook has a double hook shape which first of all stands up toward the bob weights <b>14</b> to act as an end stop as indicated previously but which then bends over in the opposite direction to act as an engagement ramp for said link rod <b>18</b>. This rod can thus return to the tongue <b>19</b> after having left it, in order to slide along it in the continuation of its movement as will be explained later on.

Whereas the linkage <b>9</b> acts as an actuator to bring about the rotation of the bob weights <b>14</b> and, as a result, of the gears borne by the control spindle <b>13</b>, the assembly made up of the tongues <b>19</b> and the crank pins <b>17</b> acts as an additional actuator for rotating these bob weights by transmitting to them, under certain operating conditions, the torque that is supplied by the return springs mounted on the tongue spindles <b>20</b>.

Whereas <figref idref="DRAWINGS">FIG. 4</figref> shows the relative position of all the elements involved in controlling the pitch of the propellers <b>6</b>, in cruising operation, <figref idref="DRAWINGS">FIGS. 5 to 9</figref> detail how this position changes during a shift into reverse from low idle on the ground (<figref idref="DRAWINGS">FIG. 5</figref>) to the reverse position (<figref idref="DRAWINGS">FIG. 9</figref>). These figures also show, top right, the orientation of the propeller with respect to the zero-pitch setting and the pitch angle β of this propeller.

In <figref idref="DRAWINGS">FIG. 4</figref>, which illustrates cruising operation, the bob weights <b>14</b> are in a part-way-up position, a position of equilibrium imposed by the position of the linkage <b>9</b>, the equilibrium being the balance between the centrifugal force exerted by the rotation of the ring <b>12</b>, which has a tendency to drive the bob weights upward, and the traction imposed by the linkage <b>9</b>, which opposes this rotation. This position of the bob weights corresponds to an angular position of the spindle <b>13</b> that gives the propeller the pitch setting β demanded by the control system <b>10</b>, which is somewhere between the low-pitch position and the high-pitch position. It may be noted that, in this position, the crank pin <b>17</b> is not in contact with the first tongue <b>19</b><i>a</i>, its link rod <b>18</b> being free to position itself against the bob weights <b>14</b> and to accompany any rotations demanded by the control system <b>10</b> of these bob weights and of the control spindle <b>13</b>. The two tongues <b>19</b> are returned toward the control spindle <b>13</b> by their torsion return spring and adopt a standby position in which each is in abutment against a spur <b>22</b> borne by the retaining ring <b>12</b>.

In <figref idref="DRAWINGS">FIG. 5</figref>, the propeller is in a position corresponding to the position of low idle on the ground, during landing, which corresponds to the low-pitch position. The pitch angle β has decreased by comparison with the value it had in cruising flight and the bob weights <b>14</b> have moved toward the bottom of the figure, i.e. in the direction toward zero pitch. In this position, the crank pin <b>17</b> has moved closer to the tongue <b>19</b><i>a </i>and its link rod has come into contact therewith. For the moment, no load is applied by the tongue to the link rod, this tongue still resting against the spur <b>22</b>.

In <figref idref="DRAWINGS">FIG. 6</figref>, the propeller is in an intermediate position in its rotation to shift into reverse, in response to traction applied by the control system <b>10</b> to the linkage <b>9</b>. The bob weights <b>14</b> have moved beyond the position of low pitch, although the pitch angle is still positive. By comparison with <figref idref="DRAWINGS">FIG. 5</figref>, the link rod <b>18</b> has slid along the tongue <b>19</b><i>a</i>, which remains resting against the spur <b>22</b>, and has come into contact with the lip formed by the hook <b>21</b><i>a </i>of this tongue.

In <figref idref="DRAWINGS">FIG. 7</figref>, the propeller is in a position that is even further advanced toward zero pitch, while still maintaining a positive pitch angle. The crank pin <b>17</b>, the free end of which is immobilized by the hook <b>21</b><i>a</i>, has performed a rotation which now brings it substantially perpendicular to the first tongue <b>19</b><i>a</i>. This rotation has been possible only through a thrusting action of the crank pin on the tongue <b>19</b><i>a </i>which moves away from the spur <b>22</b>. The torsion return spring situated on the spindle of the tongue is therefore compressed and its return force, in response, causes the tongue to thrust against the crank pin <b>17</b> and, ultimately, against the bob weights <b>14</b>.

In <figref idref="DRAWINGS">FIG. 8</figref>, the propeller is in the zero-pitch position, the position of the bob weights corresponding to their position that is unstable in terms of rotation about the control spindle <b>13</b>, under the action of centrifugal force. The free end of the crank pin <b>17</b> and the link rod <b>18</b> are still restrained by the hook <b>21</b><i>a</i>. In this situation the linkage <b>9</b> is pulled to the maximum and its orientation is such that it points toward the control spindle <b>13</b>; it therefore no longer has any action in driving the rotation of the bob weights <b>14</b> and cannot allow them to pass through the bottommost point in order to arrive at negative pitch settings. By contrast, the geometric configuration given to the crank pin—tongue assembly is such that the force applied by the tongue does not pass through the control spindle <b>13</b> and pushes the bob weights beyond their present position. The bob weights <b>14</b> cannot therefore remain in this unstable position, this being the stated objective of the invention.

In <figref idref="DRAWINGS">FIG. 9</figref>, the propeller is in reverse. The devices contributing to controlling the pitch thereof are in a position that is symmetrical with that that they have in low idle on the ground, under normal use. The bob weights <b>14</b> are in a mid-way-up position, in equilibrium between a centrifugal force that has a tendency to move them toward feathering with negative pitch angles, and traction of the linkage <b>9</b> which fixes their position so that the pitch angle in reverse corresponds to that which gives the engine the best reverse thrust. The crank pin <b>17</b> has been driven by the bob weights <b>14</b> and has escaped the action of the hook <b>21</b><i>a </i>of the first tongue <b>19</b><i>a</i>; it has slipped under the second tongue <b>19</b><i>b</i>, the one associated with negative pitch angles, using the ramp of the hook <b>21</b><i>b </i>thereof. As in <figref idref="DRAWINGS">FIG. 5</figref>, the link rod <b>18</b> is bent back against the bob weights <b>14</b> under the action of the second tongue and the return spring thereof and the second tongue <b>19</b><i>b </i>rests against the corresponding spur <b>22</b>.

The way in which the control device according to the invention works will now be described with detailed attention given to the change in pitch angle of the propellers of a high-speed propellers engine shifting from the cruising position to the reverse position so that the aircraft can land.

In normal operation, in cruising flight or during the final approach before landing, the pitch angle of the propellers <b>6</b> is somewhere between the low-pitch position and the high-pitch position, in a configuration described in <figref idref="DRAWINGS">FIG. 4</figref>. The bob weights <b>14</b> are restrained by the linkage <b>9</b> which prevents them from moving into the feathering position under the action of the centrifugal force applied to them. The crank pins <b>17</b> are free to rotate about the journal <b>16</b> of the bob weights and the link rod <b>18</b> does not interfere with the first tongue <b>19</b><i>a</i>. The pitch angle of the propellers is usually set by action of the linkage <b>9</b> on the bob weights, without the device for assisting in shifting into reverse playing any part in this.

After the aircraft has landed, the pilot throttles back and brings the engine to low idle, which results in the propellers being set to the low pitch angle position illustrated in <figref idref="DRAWINGS">FIG. 5</figref>. In order to achieve that, the control system <b>10</b><i>a </i>has pulled on the linkage <b>9</b> and caused the bob weights <b>14</b> to rotate toward a position corresponding to a pitch angle of 30°. In this position, the crank pins <b>17</b> have arrived in a bottom position, in which the link rod <b>18</b>, by design, comes into contact with the first tongue <b>19</b><i>a</i>. This contact between the link rod <b>18</b> and the first tongue occurs more or less in the middle of this tongue, without any pressure yet being applied between the two components.

The pilot then begins the shift into reverse by commanding the control system to pull on the linkage <b>9</b> to bring it into its most retracted possible position in relation to the bob weights <b>14</b>. These then rotate toward their position corresponding to zero pitch angle, trailing in their wake the crank pins <b>17</b> and the link rod <b>18</b>. The latter slides first of all along the first tongue <b>19</b><i>a </i>until it becomes wedged against the hook <b>21</b><i>a </i>(the position illustrated in <figref idref="DRAWINGS">FIG. 6</figref>). Beyond this position, as the bob weights <b>14</b> continue to rotate, they carry with them the crank pins <b>17</b> which gradually push on the tongue <b>19</b><i>a</i>, separating it from the bob weights and compressing the torsion return spring situated on the rotation spindle <b>20</b> thereof (cf. <figref idref="DRAWINGS">FIG. 7</figref>).

Because of the continuing action of the linkage <b>9</b>, the bob weights arrive at a position of symmetry about the median plane of the retaining ring <b>12</b>, which corresponds to their position of unstable equilibrium (cf. <figref idref="DRAWINGS">FIG. 8</figref>). In this position, the linkage <b>9</b> is pulled to the maximum extent by the control system <b>10</b> and finds itself pointing in the direction of the control spindle <b>13</b>; it therefore has no further effect on the rotation of the bob weights <b>14</b> and cannot prolong it with additional pulling. By contrast, when the bob weights are in this position of unstable equilibrium, the crank pins <b>17</b> receive thrust from the first tongue <b>19</b><i>a</i>, which originates from the reaction torque provided by its torsion spring. This thrust is not itself oriented toward the control spindle <b>13</b> but points to the side of negative pitch angles. The bob weights are thus made to continue their rotation and to escape from this position of unstable equilibrium, and this provides a solution to the technical problem that the invention set out to address.

From there, the centrifugal force applied to the bob weights <b>14</b> naturally causes them to continue the rotation which increases the pitch angle of the propellers, in the direction of negative pitch angles. The linkage <b>9</b> is left free so as to allow this movement to occur until a preprogrammed angular position is reached. This rotation moreover causes the link rod <b>18</b> to escape from the hook <b>21</b><i>a </i>of the first tongue, and this link rod then comes up against the hook <b>21</b><i>b </i>of the second tongue <b>19</b><i>b</i>. The ramp shape given to the end of the hook allows this rod <b>18</b> to slide along it and to slot in between the second tongue <b>19</b><i>b </i>and the bob weights <b>14</b>, thus setting in place the elements needed to ensure that the bob weights will move through their point of unstable equilibrium on the return to normal control.

The system comes to rest in a position in which the linkage <b>9</b> blocks any subsequent movement and compensates for the action of this centrifugal force (cf. <figref idref="DRAWINGS">FIG. 9</figref>). The position adopted is chosen by the designer of the device to give the propellers a pitch angle of a magnitude that provides the best reverse traction, bearing in mind the engine speed imparted to the engine in the reverse situation. As depicted in <figref idref="DRAWINGS">FIG. 9</figref>, without this value being an imperative, the reverse pitch angle corresponds, in negative, to the pitch angle for low idle on the ground (−30°).

The return to the normal use position takes place in a similar way, the movement through the point of unstable equilibrium being achieved by virtue of a thrust generated by the second tongue <b>19</b><i>b</i>, which acts in the same way as the first tongue <b>19</b><i>a </i>did during the shift into reverse, but pressing this time against the hook <b>21</b><i>b </i>of the second tongue <b>19</b><i>b. </i>